Is the the pulse tube cooler a
must or is it simply better for
the MICE AFC module?
Michael A. Green
Lawrence Berkeley Laboratory
Berkeley CA 94720, USA
MICE Collaboration Meeting CM-15
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What are the Cooler choices
for the AFC Module?
• The AFC module has the need for three coolers.
Two coolers are needed for the superconducting
magnet and one cooler is needed for the absorber.
• The coolers for the MICE AFC module will be will
deliver 1.5 W at 4.2 K and > 40 W at 55 K.
• Two types of coolers can be used. These machines
are the Sumitomo RDK-415D GM cooler or the
Cryomech PT-415 pulse tube cooler.
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Cryomech PT415 Cooler
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PT415 Pulse Tube Cooler in its Test Stand
Surge Tank
Rotary Valve
Test Cryostat for Machine
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Computer Display of the PT415 Cooler in Operation
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Operating Points of the PT415 Cooler
SECOND STAGE TEMPERATURE, K
SECOND STAGE TEMPERATURE K
6
6
55
44
33
22
25
0 W 21W
3.0W
84W
63W
42W
2.5W
2.0W
1.5W
1.0W
0.5W
0W
CRYOMECH
TEST
35
45
55
65
75
FIRST STAGE TEMPERATURE, K
The measured test data is from Tom Painter of Florida State University.
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PT415 Cooler Rotary Valve and Motor
Rotary Valve Motor
Rotary Valve
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Typical Tube Cooler Compressor Package
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A Comparison of the PT415 Cooler
with the RDK-415D Cooler
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Advantages of the Pulse Tube Cooler
•
•
•
•
•
•
•
•
•
More cooling on 1st stage at a given temperature.
Faster cool down of cooler and load.
Same performance at 50 Hz as at 60 Hz.
There is lower cold head vibration (a factor of >30).
There is a longer maintenance interval with less
loss of performance between maintenances.
Can use snap-in integration with a magnet.
Remote valve motor permits cold head operation in
magnetic fields of 1 to 2 T.
Liquefaction rate is higher than other cooler types.
Lower magnetic distortion due to cooler pulsation.
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Advantages of the GM Cooler
• Orientation of the cooler cold head is not an issue.
• Cooler cold head assembly is smaller.
• Compressor module takes up less space.
• There is lower input power to the compressor for a
given amount of refrigeration. As a result, less
cooling water needed for the compressor.
• The machine capital cost is lower.
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Performance Comparison of the RDK-415D
and the PT415 Coolers at 50 Hz
PT415
Sumitomo
RDK415
normal
Remote*
1st Stage Temp @ 40 W (K)
54
40
43
2nd Stage Temp @ 1.5 W (K)
4.2
4.2
4.35
Base Temperature (K)
~2.9
~2.8
~3.0
Input Power @ 50 Hz (kW)
6.5
10.5
10.5
Machine Efficiency (%)
~4.4
~3.5
~3.3
Parameter
* The remote valve is 1.0 meters from the cooler cold head.
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Size Comparison of the RDK415D
and the PT415 Coolers
PT415
Sumitomo
RDK415
normal
Remote*
To p Flange to 1st Stage (mm)
156.0
195.7
195.7
1st Stage to 2nd Stage (mm)
236.5
212.4
212.4
To p Flange Diameter (mm)
180.0
186.7
186.7
1st Stage Diameter (mm)
126.0
129.5
129.5
2nd Stage Diameter (mm)
58.0
94.0
94.0
Cold Head Height (mm)
557.0
759.0
414.4
Cold Head Length (mm)
294.0
339.0
186.7
Parameter
* The remote valve is 1 meter from the cold head. The buffer tank is
with the remote rotary valve. The cold head height is the top flange
and the cold parts of the machine.
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The Magnetic Field on the Cooler
Is it an important issue?
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Places where Magnetic Field is a Concern
Displacer Motor <0.08 T
Valve Motor <0.1 T
Displacer <0.08 T perpendicular
Displacer <0.3 T parallel
Regenerator <1.5 T
PT415 Pulse Tube
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Worst Case Field Map Flip Mode for AFC Module (radial)
From H. Witte & J. Cobb Oxford University
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Worst Case Field Map Flip Mode for AFC Module (axial)
From H. Witte & J. Cobb Oxford University
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Worst Case Field Map Non-flip Mode for AFC Module (radial)
From H. Witte & J. Cobb Oxford University
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Worst Case Field Map Non-flip Mode for AFC Module (axial)
From H. Witte & J. Cobb Oxford University
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The Cooler Magnetic Field Issue
A magnetic field on the cooler
motors causes the motors to
stall. The RDK-415D AC motor
is a little more sensitive to field
than the PT415 stepper motor.
Neither motor will operate in
fields much above 0.1 T. Motor
shielding is an option for both
coolers.
RDK-415D Displacers from Y. Matsubara
ICEC-20 Proceedings (2005) p 189
Magnetic field saturates the
regenerator material at ~1.5 T.
This reduces the output at 4.2 K
10 to 15 percent.
A magnetic field perpendicular to the moving
displacer increases wear and reduces the GM cooler
maintenance interval. The field parallel to the
displacer can be four times the perpendicular field.
MICE Collaboration Meeting CM-15
Private communication
Geoff Green, NRL
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PT-410 Pulse Tube Cooler Valve Motor
The PT410 or PT415 valve motor can be shielded to operate in a field of 0.5 T.
Cryomech will provide a custom shield for the valve motor at minimal cost.
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PT415 Cooler Remote Motor without Surge Tanks
Rotary Valve Motor
Rotary Valve
The surge tank should be attached to the rotary valve.
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Comments on Magnetic Shielding
• Iron shielding of the displacer tube on a GM cooler
is difficult. The field perpendicular to the tube
must be kept below 0.08 T for long life.
• Iron shielding of the rotary valve on a pulse tube
cooler is easier than shielding the motor assembly
of a GM cooler. The valve motor shield would be
included with the pulse tube cooler.
• The rotary valve can be moved to a low field region
away from the cooler by 1 meter if the field at the
valve is greater than 0.4 to 0.5 T
• Shielding of the 2nd stage regenerator is not
necessary if the field on the regenerator is <1.5T.
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Snap-in Integration of the
Pulse Tube Cooler to the Magnet
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Snap-on Coolers for the Magnets
• Since the magnets will be cooled down with liquid
cryogens, the pulse tube coolers can be installed in
the magnets just before they are cooled down.
• The condenser is attached to the second stage of
the PT cooler. (This is included in the price of the
cooler.) The PT cooler is connected directly into
the LHe space of the cryostat. The PT cooler will
reduce the cooler neck heat leak over a factor of 5.
• The PT coolers can be removed without warming
up the magnets. A new cooler can be installed and
cooled down without warming the magnets
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2nd Stage Cold Head Helium Condenser
Q/A = ~40 W m-2
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Snap-on Integration continued
• Snap-on integration is doable when GM cooler is
used. The cooler neck heat losses are much higher.
This will affect the overall performance of the cooler
and magnet combination.
• Snap-on integration of a PT cooler to the absorber is
possible provided one can eliminate air leaks into the
hydrogen space. An liquid absorber cooler should
be designed for hydrogen and helium liquefaction. I
am willing to work with Cryomech to see how this
might be accomplished safely.
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Hydrogen and Helium Liquefaction
with a Pulse Tube Cooler
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The H2 and He Liquefaction Problem
• The goal is to fill absorber with LH2 using the cooler
in 15 to 24 hours. One wants to fill the absorber with
LHe in about 24 hours using the cooler.
• This means that the H2 or He gas must be pre-cooled
by the cooler before it can be liquefied*. The precooling rate is >100 W for H2 and >50 W for He.
• The pre-cooling is applied through a heat exchanger
attached to the 1st stage or the tube between the 1st
and 2nd stages and or a liquid nitrogen pre-cooler.
• The heat exchangers can not be part of the hydrogen
vent circuit.
* See MICE notes 108 and 113 concerning the need for this heat exchanger.
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Why is the type of cooler used important?
• The only way that one can pre-cool the gas being
liquefied using a GM cooler is to attach a laminar
flow heat exchanger to the 1st stage. LN2 cooling
should also be used.
• With a pulse tube cooler, one can pre-cool off of the
regenerator tubes of both stages. Liquefaction
using the pulse tube cooler is much more efficient.
• Using the pulse tube cooler, the neck heat leak into
the cryostat is reduced by over a factor of five.
This benefit is not available from a GM cooler.
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The Cryomech PT410 used as a Liquefier
Refrigeration from the PT-410 Cooler (W)
1.0
•
A PT-410 cooler (1 W @ 4.2 K) was
used. The actual cooler capacity is
not known
•
Input power = 8 kW @ 60 Hz
0.6
•
Liquefaction into a 60 liter storage
dewar. The heat leak into the
dewar is unknown
0.4
•
The liquefaction rate for helium gas
was 15.2 l/d (0.022 g/s).
•
Dewar cool down took ~20 hrs
until liquid accumulation starts.
The start temperature is not
known.
•
The data was published in
Cryogenics 45 (2005), pp 719-724
2 liters per day (G = 42.8 j/g)
0.8
5 liters per day (G = 38.9 J/g)
0.2
0.0
0.000
0.005
0.010
0.015
0.020
0.025
Helium Liquefaction (g/s)
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The Cryomech Helium Liquefier
Now a Commercial Product
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PT410 Helium Liquefier for the South Pole Dewar
Liquefaction Pot
2nd Stage
Helium Heat
Exchanger
Pulse Tubes
1st Stage
Rotary Valve Assembly
1st Stage Tubes
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60 He Liter Test Dewar for the
South Pole Station PT410 Helium Liquefier
In a wide mouth 60 liter dewar, the He liquefier
makes up to 15 liters per day. The 4000 liter
South Pole dewar had a boil off rate of 14 liters
per day w/o a cooler. With the PT410 liquefier,
there is a net liquefaction of 2 to 3 liters per day.
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He Liquefaction using a Pulse Tube Cooler, Two GM
Coolers and Two GM Coolers with a J-T Circuit
Cryomec h
PT410
Sumitomo
K300
4110
GM+JT
Liquefaction Rate (L d ay-1)
15.2
6.0
8.0
Liquefaction Rate (g s-1)
0.022
0.0086
0.0116
1
2
2
4.2 K Refrigeration (W)
1.0
3.0
~2.0
Input Power (kW)
8.0
15.0
8.0
Liquefaction Coefficient (J g -1)
~45
~350
~130
Parame ter
Number of Coolers
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Capital Cost and Operating
Cost Issues
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Cooler Cost and Other Related Issues
• The manufacturer’s list price in the US for a 1.5 W
Sumitomo GM cooler is 37.5 k$. The list price for
the Cryomech PT cooler is 46.0 k$. The cooler list
price is like the MSRP on a car. The price can be
negotiated lower, particularly when one orders
multiple coolers.
• Part of the PT cooler higher price is the larger He
compressor. The PT cold head is simpler, so its cost
should be lower. Much of the higher price for the
PT cooler is due to the lower production rate at
Cryomech (500 units per year versus 10000+ units
per year at Sumitomo).
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Cost and other issues continued
• The capital cost of the cooler is not the only thing
that should be considered. The maintenance
interval and the cost of maintenance should also be
considered.
• The method of installation of the cooler on the
magnets will affect the cost of the magnet cryostat. I
believe that the use of the PT cooler on the magnets
will reduce the cost of the magnets enough to offset
the increased cooler price.
• The PT compressor can be located 30 to 40 meters
from the cooler cold head.
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Concluding Comments
• The PT415 cooler is now in production.
• The PT415 cooler is larger than the RDK-415D
GM cooler. The diameter of the top flange is
not very different. The cold portion of the PT
cooler is not very different either.
• Pulse tube coolers are less sensitive to magnetic
field, particularly when a remote valve is used.
• Snap-in installation into the magnets is a plus.
More engineering is needed to see if this feature
can be applied to the absorbers.
• Pulse tube coolers work very well as liquefiers.
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Is the the pulse tube cooler a must or is it
simply better for the MICE AFC module?
In my opinion, the pulse tube cooler is a
must if one wants to fill an absorber using
the cooler. For the magnets, the pulse tube
cooler is better in many respects, but not all.
The pulse tube cooler is a must
for the coupling coils.
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